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How To Get Rid Of Rising Damp

Take steps to rid the home of this common problem to prevent structural damage

Flaking paint and damaged surfaces are the end result of rising damp

You can often smell and sense damp before you can see it. When it finally does appear it’s a costly, unhealthy nuisance that has to be dealt with fast.

Rising damp destroys the comfort of a home, creating musty smells and causing or aggravating asthma and allergies.

If left untreated, rising damp can carry soluble salts up into the masonry, causing what’s known as efflorescence, which can eventually destroy foundations and in severe cases result in once solid masonry eroding and crumbling away.

Right now parts of Australia are in the grip of a rising damp and mould scourge. According to Scott Lambert, national managing director of Dr Damp, it’s the worst he’s seen in 15 years of business.

To treat rising damp it’s necessary to identify the source and apply the appropriate solution

A damp epidemic

‘Three years ago, one in 20 of the homes we visited had mould, now it’s four out of five,’ says Dr Damp’s Scott Lambert. ‘It’s an epidemic.’

‘Sydney seems to be the worst because of recent rain and heat. Melbourne’s had a drenching but as it’s colder the problem isn’t as bad.’

Scott says the parts of Australia where heat and moisture are most common, such as the Northern Territory and tropical Queensland, don’t have mould problems.

‘Places like Darwin with a wet, humid season aren’t affected because houses are well ventilated and often built off the ground.

‘Good ventilation is the main cure to damp. You should open up the house to ventilate against dampness.’

The hidden causes

Mould is a living organism that blows in from outside and is fairly harmless unless it comes into contact with moisture. When the two combine, the dampness feeds the mould.

Scott says a mould detector placed against a wall can sense if there’s a problem before it starts to show.

‘Most people think rising damp comes up the walls but in 90% of cases the moisture comes off the ground. Rising damp happens when moisture sits under a house then the sun comes out causing humidity.’

It can also provide a breeding ground for pests. ‘Structurally these conditions are a magnet for termites that feed off damp timber and cockroach infestations are also likely.’

TIP Tackle damp-prone areas of the house such as kitchens and bathrooms with specialist paints and primers designed to combat damp and mould.

Solution 1: Underfloor ventilation

For houses with an underfloor cavity, restoring and maintaining the underfloor ventilation may be enough to fix a damp problem.

Damp air is removed from under the floor using a circulation pump and replaced with fresh, dry air that is forced to move in a drying pattern through the damp air space.

The pattern is calculated based on air volume and an environmentally friendly air pump ensures the correct amount of circulation occurs.

To install in some homes, large vents about a metre apart improve the airflow sufficiently to keep the subfloor dried out. But for situations with permanently damp soil, mechanical ventilation may be needed.

While this will cost in the thousands, it eliminates conditions where termites can flourish, so can save money in the long run.

TIP When renovating, maintain or repair a ventilated timber floor rather than replacing it with a concrete slab poured on sand or fill.

Solution 2: Damp proof course

A physical DPC, often made of thick black polyethylene sheeting, is inserted about 200mm above ground level for external walls and as close to the floor level inside.

It prevents moisture rising from the ground into the walls but can be time-consuming and costly to DIY.

While it’s still the preferred option for salt-laden damp, a chemical DPC may be easier for other situations.

To install the DPC is positioned by replacing the base of the wall section by section, or removing and repacking a horizontal mortar joint.

At the same time, drainage should be added outside the wall and garden beds moved to at least 300mm from the wall to minimise moisture.

Scott says, ‘Physical damp proof coursing starts from about $150 a linear metre. If it’s an area as small as a metre it could even cost as much as $1000 a linear metre depending on the severity and difficulty of the job.’

Solution 3: Chemical damp proof course

The main advantage of chemical DPCs is minimal disruption to masonry as water-repellant chemicals are inserted into a series of drilled holes along the wall base or mortar.

To install, chemicals are injected by pressure or using gravity-fed feeder bottles then moved rapidly into the masonry pores where the solution cures internally over two to six weeks.

Chemical DPCs should be applied by professionals to ensure they penetrate the entire wall thickness.

To cost it is difficult, due to variables such as the type of brick, location and size of the job.

According to Dr Damp technician Tony Long, ‘Costs start at $75 a linear metre and go up to $300 a metre.’

Tony adds that each state’s brickwork makes cost estimates even trickier to determine. ‘South Australia has a soft type of brick, in Queensland and Victoria they have bricks with about 12 holes in the centre and they’re hard to do, so it’s not measured per linear metre.’

Spotting signs of damp

To combat damp, check around the house twice a year, looking for blocked vents, leaking pipes and roofing, and mortar crumbling from joints. Here are six common signs of damp and their solutions:

1. Mouldy brick

Dampness rises up a wall when the flooring is solid, as moisture has nowhere to escape. Fix it by replacing the damp proof course.

Mouldy brick can be fixed by replacing the damp proof course

2. Leaking gutter

Water can creep down from gutters and downpipes. Fix it by ensuring flashing is in position, fixing gutters and using sealant if needed.

Fix gutters to prevent any leaks

3. Discoloured grout

Dampness can seep through gaps between tiles. Fix it by regrouting and resealing so there are no gaps around the tiles.

Regrout the gaps around tiles to stop damp setting in

4. Peeling plaster

The plaster peels away and doesn’t maintain adhesion to a completely damp wall. Fix it by replacing the damp proof course.

Plaster can peel away from damp walls

5. Mildew on walls

Warm, damp bathrooms encourage mould. Fix it by using an anti-mould spray, ventilating and wiping walls dry after showering.

Mildew can be cleaned away with an anti-mould spray

6. Tide marks

Paint and plaster show water stains and peeling. Fix this by checking for and treating the source or replace the damp proof course.

Paint will start to peel and flake off the walls if it gets damp

Treat efflorescence

Damage occurs when soluble salts in the wall materials become moist then dry out, forming a shiny surface layer called efflorescence. If the layer crystallises it can erode even the strongest materials.

Treatment begins with fixing leaks and a new damp proof course. Regular maintenance should be done on plumbing, clearing the roof and gutters, plus checking potential drainage or underfloor ventilation.